The present invention relates generally to the end support section of the superheater or reheater tubes, which includes a bend area and a supporting member. The bend area and the supporting member are integrally formed, molded or cast of suitable material, such as the material used to construct the tubes.
Superheaters and reheaters can be broadly described as single-phase heat exchangers with steam flowing inside the tubes and flue gas passing outside, generally in crossflow. These devices are used to increase the temperature of saturated steam, thereby increasing its thermal energy. Thus, superheaters and reheaters are located in zones of high gas temperature. Due to their high operating temperature, it is preferable to transfer the major support loads of these devices to the steam tubes themselves.
Boiler manufacturers have used stainless steel attachments welded to the ends of superheater tubes as supports. These attachment welds add a high stress to the bend area of the tubing and this often causes failure of the bend or weld in service. Failure causes the steam tubes to lose support and can cause tube leaks that lead to unwanted boiler forced outages. In addition, welding tube support attachments is extremely labor intensive, and the attachments generally do not remain on the tubes for a long period of time. It is difficult, if not impossible, to perform maintenance on or to repair the tube support attachments in the boiler because they are not easily accessible. Furthermore, welds may have to be heat treated for some alloys. Also, the tube support attachments cannot withstand high temperatures, i.e., above 1400 degrees fahrenheit, unless cooling is used. As a result, welded support attachments are expensive to install, operate and maintain, and lack the durability needed to support steam tubes that are subjected to elevated temperatures.
Accordingly, a need remains for an end support capable of overcoming one or more of the above-mentioned disadvantages. The end support of the present invention is integrally formed, molded or cast as a single body from suitable material, such as steel alloy. The end support of the present invention is also more economical to install and more durable than the prior art.
Additional details relating to superheater or reheater design can be found in Chapters 1, 7 and 19 of Steam/its generation and use, 41th Edition, Stultz and Kitto, Eds., Copyright ©2005, The Babcock and Wilcox Company, the text of which is hereby incorporated by reference as though fully set forth herein.